This invention relates to a method and apparatus for baseline restoration in AC-coupled signals, and more particularly to a circuit for restoring the DC reference of random signals.
Whenever random codes are serially transmitted through an AC-coupled system, such as an FM radio link, there will exist at the receiving terminal a continually varying DC offset with respect to the originally transmitted signal. This random modulation of the DC reference is commonly referred to as a "galloping baseline" which, at any one instant, may be viewed as a fixed baseline offset of the signal relative to a reference.
In all practical systems, it must be assumed that the transmission link is limited in bandwidth and is fully capable of modulating the signal with some form of noise. The interpretation of a signal distorted by noise in such a transmission link is greatly aided if the true baseline of the modulated signal is known. An object of this invention is to provide an improved circuit for restoring the baseline of an AC-coupled signal.